1. Field of the Invention
This invention relates generally to microwave power sources and more particularly to microwave tubes which utilize crossed electric and magnetic fields during operation.
2. Description of the Prior Art
The most common varieties of microwave power tubes are classified as either linear beam tubes or crossed-field tubes. Linear beam tubes feature electric and magnetic fields which are parallel to one another. The magnetron is a popular, well-known example of a crossed-field tube. In the magnetron and other crossed-field tubes a DC electric field is oriented perpendicular to a constant magnetic field. Typically, a high magnetic field, on the order of 1000-3000 Gauss is employed. Thermionic electrons, moving under the influence of perpendicular electric and magnetic fields, induce RF radiation in a plurality of resonant cavities. The RF radiation is excited by angular bunching of the electrons. Radiation is extracted from one of the cavities to power an antenna, warm leftovers, etc. Control of the modes excited in the various magnetron cavities has always presented a problem for the designer. Strapping of adjacent cavities provides some control over the modes of oscillation. However, the fundamental laws of electrodynamics require that transverse electromagnetic modes (TEM) cannot exist in the magnetron's resonant cavities. Consequently, some care must be used in coupling the magnetron's output power if a TEM output into, for example, a coaxial transmission line, is desired.